Diesel engines are internal combustion engines that combust an air and fuel mixture reciprocally drive pistons slidably disposed within cylinders producing drive torque. Diesel engines typically have a higher efficiency than gasoline engines due to the increased compression ratio of the diesel combustion process and the higher energy density of diesel fuel. Consequently, diesel engines commonly achieve better gas mileage than equivalently sized gasoline engines. Vehicle manufacturers incorporate emission control devices into the exhaust treatment systems of diesel engines to reduce emissions.
An exemplary exhaust treatment device includes a diesel oxidation catalyst (DOC). A DOC is an exhaust flow through device that includes a honey-comb formed substrate having a large surface area coated with a catalyst layer. The catalyst layer includes precious metals including, but not limited to, platinum and palladium. As the exhaust flows over the catalyst layer, carbon monoxide, gaseous hydrocarbons and liquid hydrocarbon particles are oxidized to reduce emissions.
The DOC may be adversely affected when the temperature of the exhaust exceeds a threshold. Inlet and outlet temperature sensors are typically associated with the DOC to monitor exhaust temperatures. Proper functioning of the temperature sensors is required to enable the vehicle control system to monitor exhaust temperature. Because the temperature sensors work over a large operating range (e.g., −40° C. to 800° C.) it has traditionally been difficult to ensure accuracy over the entire range.